1. Field of the Invention
This invention relates to the field of medical electronics and in particular to improved devices for handling electrical leads with a minimum of trauma to the body tissue in which the electrical leads are implanted.
2. State of the Prior Art
Electrical stimulation of body tissue and organs as a method of treating various pathological conditions is becoming quite commonplace. Such stimulation generally entails making some type of electrical contact with the body tissue or organ. In particular, with respect to the heart, electrical leads have been implanted by a thoracotomy in which an electrode formed on the end of the lead are physically implanted into the myocardial tissues.
Various electrode structures and various techniques for implanting those electrode structures into such body tissue as the heart or myocardium, have been developed. Typically, electrodes attached to the heart are stimulated by a cardiac pacemaker which may be implanted within the patient's body. Previously, a thoracotomy was commonly required to attach the cardiac pacemaker leads to the heart, and the electrical leads were sutured into electrical contact with the heart. This technique has numerous disadvantages. Firstly, a thoracotomy, which requires a large incision in the chest or thorax, is drastic surgery and has a relatively high mortality rate. Secondly, suturing the electrical leads into electrical contact with the heart causes severe trauma to the heart, which it is desirable to minimize.
An intravenous connection has also been used to attach electrical leads of a cardiac pacemaker to the heart. In this technique, the electrical lead is passed through a vein into the heart where it is held by fibrilla located in close proximity to the heart valve through which the lead is passed. There are, however, many disadvantages to this technique also, including: the possibility of damage to the vein during insertion, such as vein perforation; the failure to attach securely the electrical lead to the heart; the possibility of perforating the heart wall with the electrical lead during insertion or after attachment has been completed; and the possibility of improper lead placement in the heart.
In U.S. Pat. No. 3,737,579, assigned to the assignee of this invention, there is disclosed a unipolar body tissue electrode comprising an uninsulated, conductive, rigid helix adapted for attachment to body tissue and a flexible insulated conductor having a proximal end adapted for connection to a pacemaker and a distal end for connection to the helical electrode. Further, the noted patent describes a device or auxiliary tool having an elongated, cylindrical configuration. At one end thereof there is provided a slot or cavity for receiving a raised portion or boot of the lead surrounding and housing a portion of the helical electrode, and further a groove aligned with the axis of the auxiliary tool for receiving at least a portion of the length of the leads insulated conductor. The lead is mounted in the auxiliary device as indicated and the helical electrode is inserted by rotating the auxiliary tool. After the helical electrode has been inserted into the body tissue, the insulated conductor is stripped from the axially aligned groove and the boot is removed from the cavity.
In U.S. Pat. No. 3,875,947, assigned to the assignee of this invention, there is described an unipolar, tissue electrode similar to that described in U.S. Pat. No. 3,737,579, and further an improved auxiliary tool for facilitating the removal of the electrical lead from the primary tool after its helically shaped electrode has been inserted into body tissue, e.g. myocardium. In particular, the tool comprises a handle or primary tool of a substantially cylindrical configuration having a bore running along the axis thereof into which a secondary tool or tunneling rod is inserted, and a groove in communication with the bore extending also along the axis of the handle. The tunneling rod includes ridge or fin portions that are disposable in the groove and serve to remove the lead from the primary tool after electrode implantation. Further, the leading end of the tunneling rod is pointed to permit removal of the lead's boot that receives a portion of the helical electrode. In operation, the electrode is mounted as indicated above and the surgeon inserts the helical electrode by rotating the handle with the electrode mounted therein. After implantation, the surgeon inserts the tunneling rod into the bore directing the rod along the length of the handle whereby the fin is moved through the groove thus removing the lead's insulated conductor and upon full insertion, the leading end of the tunneling rod displaces the electrode's boot from the cavity.
As set out in an article entitled, "An Improved Introducer for the Sutureless Myocardial Pacemaker Lead", by Dr. Gerald M. Lawrie et al., appearing in The Annals of Thoracic Surgery, Volume 23, No. 5, May, 1977, a disadvantage of the inserting device of the U.S. Pat. No. 3,875,947 is that is requires a bimanual operation, i.e. the attending surgeon is required to grip the handle with one hand, while pushing forward the tunneling rod with his other hand to remove the insulated conductor. In addition, as the leading portion of the tunneling rod pushes the insulating boot of the electrode from the cavity, a rotating motion occurs, tending to displace the helical electrode within the myocardium, at right angles to the longitudinal axis of the handle. This unnecessary motion may cause myocardial trauma at the tip of the helical electrode, with subsequent fibrosis and threshold rise. To overcome these noted problems, this article suggests the adaptation of the inserting device of U.S. Pat. No. 3,875,947, by providing a series of fins in the tunneling rod and after insertion of the tunneling rod within the handling device, of placing the insulating conductor into the groove of the handle to form a plurality of loops. In addition, the leading end of the tunneling rod is shaped cylindrically whereby the attending surgeon may simply direct the tunneling rod forward with respect to the handle to remove the boot of the electrode lead, and to displace the insulated lead from the handle's slot with a single, unidirectional motion.
The forming of the loops into the noted inserting device increases the effective diameter of the device so that in a typical surgical procedure, the lead is disposed to increase the chances that it may catch on the surgeon's fingers or perhaps some portion of the exposed patient's body and be withdrawn from the groove of the inserting tool. In addition, the surgeon's attention needs to be closely directed to the relative position of the tunneling rod with respect to the handle while the lead is being inserted into the groove. In addition, after insertion, the tunneling rod is only loosely held within the handle and may through inadvertance fall out, possibly into the patient or onto the floor to be contaminated. As will be explained later, the tunneling rod may be used in a further step of the surgical procedure and if contaminated would have to be disposed.